274 
INTERNAL STRUCTURE AND 
mass of the glacier is an essential element of 
its motion, I may allude to several other well- 
known facts. The loose snow of the upper re- 
gions is gradually transformed into compact 
ice. The experiments of Dr. Tyndall prove 
that this may be the result of pressure ; but 
in the region of the n6ve it is evidently ow- 
ing to the transformation of the snow-flakes 
into ice by repeated melting and freezing, for 
it takes place in the uppermost layers of the 
snow, where pressure can have no such effect, as 
well as in its deeper beds. I take it for granted, 
also, that no one, familiar with the presence of 
the numerous ice-seams parallel to the layers 
of snow in these upper regions of the glacier, 
can doubt that they, as well as the nevS , are 
the result of frost. But be this as it may, 
the difference between the porous ice of the 
upper region of the glacier and the compact blue 
ice of its lower track seems to me evidence 
direct that at times the whole mass must as- 
sume the rigidity imparted to it by a temper- 
ature inferior to the freezing-point. We know 
that at 32° Fahrenheit, regelation renders the 
mass continuous, and that it becomes brittle only 
at a temperature below this. In other words, 
the ice can break up into a mass of disconnected 
fragments, such as the capillary fissures and the 
infiltration-experiments described in my “ Sys- 
